As a Cho gath player, how do you manage your ult ?

I think this is probably dependant on your build and match up, but do you guys just try and get as many stacks as soon as possible or do you save it for eating enemy players ? I personally think it's wasteful to ult on minions instead of using it to kill champions or epic monsters, and getting too many stacks makes you grow too big and makes it easier for enemies to hit you and cho gath isn't too tanky even if you build tank he isn't as tanky as an Ornn or Malphite cause Cho gath mostly favors stacking HP instead of armor/MR.